The present invention is related to a scanning unit for an optical position measuring device.
Known optical position measuring devices include a scanning unit which is movable in relation to a graduation scale and which is used to produce positionally dependent scanning signals. For this, a plurality of optoelectronic components, such as light sources, designed as LEDs, and detector elements, designed as photoelements, are generally configured on the scanning unit side. In this context, scanning signals, which are modulated as a function of displacement, are produced via the photoelements when the graduation of the scale is scanned. As a general rule, the photoelements are arranged on carrier elements, for example boards or printed-circuit boards designed for this purpose. The radiation-sensitive surface regions of the photoelements are oriented to face away from the carrier member. Connector leads, or bonding wires, which must be placed between the carrier element and the contacting regions of the photoelements, are used for the contacting of the photoelements. As in the case of the radiation-sensitive surface regions, the contacting regions are arranged on the side of the photoelements that faces away from the carrier element. The connector leads constituted as bonding wires must be reliably protected to ensure that no damage is caused during the measuring operation by any scale movement in relation to the scanning unit. A problem however arises especially when the optical scanning principle selected for the particular case stipulates a very small distance between the optoelectronic components and the scale that is scanned by these components.
Therefore, to protect the connector leads, the European Patent No. 0 577 088 A2 proposes arranging the photoelements on the carrier member, subsequently contacting these elements using bonding wires, and then applying a suitable transparent encapsulating material over the contacting regions and the radiation-sensitive surface regions of the photoelements. As a last step, the surface of the encapsulating material is patterned to produce the required scanning graduation. If, however, the optical scanning principle selected in the particular case requires a smallest possible distance between the radiation-sensitive surface regions of the components and the scanning graduation, then the arrangement proposed by European Patent No. 0 577 088 A2 is unsuitable. Furthermore, an arrangement of this kind requires graduation of the transparent encapsulant, and this cannot be done with the same precision as can, for instance, graduation of a separate glass scanning plate.
Equally unsuited for this kind of requirement for a small distance between the radiation-sensitive surface regions and the scanning graduation is an arrangement disclosed in U.S. Pat. No. 4,703,176. It proposes placing a scanning plate having a suitable scanning graduation at a finite distance above a plurality of optoelectronic detector elements. In this context, the scanning plate extends with its surface over the entire area of the detector elements, inclusive of the corresponding, adjacent contacting regions. The bonding wires for contacting the detector elements are protected from mechanical damage in this case by the scanning plate disposed above them. However, the distance provided between the radiation-sensitive surface regions and the scanning graduation is, again, too large for certain- optical scanning principles in particular when a compact type of construction is needed.
It is furthermore known from Japanese Patent Document No. 09-189514 to arrange a transparent glass plate over a graduated detector arrangement of a scanning unit, the glass plate being arranged and dimensionally sized to protect the bonding wires required for the contacting from mechanical damage during a measuring operation. What is problematic in this case is that the detector elements in this kind of scanning unit design already include the scanning graduation, so the result is less flexibility when designing the corresponding position measuring devices.
Fundamentally similar problems result when it is required to arrange other optoelectronic components, such as light sources having radiation-emitting surface regions, in conjunction with prearranged transmitting graduations in a compact scanning unit of an optical position measuring system.
An object of the present invention is to devise a scanning unit for an optical position measuring device, which is able to provide reliable protection from mechanical damage to connector leads even with a required small distance between the radiation-sensitive or radiation-emitting surface regions of optoelectronic components.
The present invention provides a scanning unit for an optical position measuring device, suited for optically scanning a scale graduation structure (10), to produce positionally dependent scanning signals on the basis of the scale graduation, comprising:
a) a carrier element (2; 21; 31)
b) at least one optoelectronic component (3a, 3b, 3c, 3d; 23a, 23b.123b.2, 23b.3, 23b.4, 23c; 33c, 33d), which is arranged on carrier element (2; 21; 31), a radiation-sensitive or a radiation-emitting surface region of the component (3a, 3b, 3c, 3d; 23a, 23b.123b.2, 23b.3, 23b.4, 23c; 33c, 33d) being oriented to face away from the carrier element (2; 21; 31);
c) at least one electrically conductive connector lead (6a, 6b, 6c, 6d; 26a-26i; 36c, 36d) between the carrier element (2; 21; 31) and a contacting region (5a, 5b, 5c, 5d; 25a-25i; 35c, 35d) of the component (3a, 3b, 3c, 3d; 23a, 23b.123b.2, 23b.3, 23b.4, 23c; 33c, 33d); and
d) an at least semi-transparent cover element (4; 24; 34), which
d1) at least in subregions has a graduation (7a, 7b, 7c, 7d;
27; 37c, 37d); and which
d2) is arranged directly on the radiation-sensitive and/or radiation-emitting surface region of the component (3a, 3b, 3c, 3d; 23a, 23b.123b.2, 23b.3, 23b.4, 23c; 33c, 33d) in such a way that the contacting region (5a, 5b, 5c, 5d; 25a-25i; 35c, 35d) of the component (3a, 3b, 3c, 3d; 23a, 23b.123b.2, 23b.3, 23b.4, 23c; 33c, 33d) is not covered by it; and
d3) the thickness of the cover element (4; 24; 34) is selected so as to ensure that the top side of the cover element (4; 24; 34) exceeds the height (hB) of the connector lead (6a, 6b, 6c, 6d; 26a-26b; 36c, 36d) in the contacting region (5a, 5b, 5c, 5d; 25a-25i; 35c, 35d).
Further advantageous features of the present invention include that: (a) the carrier element (2; 21; 31) may be designed as a board with signal lines integrated therein; (b) the cover element (4; 24; 34) may be made of glass; (c) the cover element (4; 24; 34) may be adhesively mounted on the component (3a, 3b, 3c, 3d; 23a, 23b.123b.2, 23b.3, 23b.4, 23c; 33c, 33d); (d) the connector lead (6a, 6b, 6c, 6d; 26a-26i; 36c, 36d) may be constituted as bonding wire; (e) an encapsulant, i.e. an encapsulating material, (8) may be arranged in the contacting region (5a, 5b, 5c, 5d; 25a-25i) of the component (3a, 3b, 3c, 3d; 23a, 23b.1, 23b.2, 23b.3, 23b.4, 23c); (f) the optoelectronic component (3a, 3b, 3c, 3d; 23a, 23b.1, 23b.2, 23b.3, 23b.4, 23c; 33c, 33d) may be designed as a light source or as a detector element; (g) the cover element (4; 24; 34) may have a graduation on- the side that faces the component (3a, 3b, 3c, 3d; 23a, 23b.1, 23b.2, 23b.3, 23b.4, 23c; 33c, 33d); (h) the graduation may be designed as a transmitting or scanning graduation scale; (i) a plurality of subregions, i.e. partial regions, having graduations (7a, 7b, 7c, 7d) may be arranged on the cover element (4); (j) a plurality of optoelectronic components (23a, 23b.1, 23b.2, 23b.3, 23b.4, 23c) may be arranged on the carrier element (21) as components integrated in a flat carrier substrate (23); (k) the cover element (24) arranged over the optoelectronic components (23a, 23b.123b.2, 23b.3, 23b.4, 23c) may bear a fine graduation (27) at least in subregions, and a plurality of components (23b.1, 23b.2, 23b.3, 23b.4) may be designed as optoelectronic detector elements that are integrated in the carrier substrate (23); (1) the cover element (34) has a pocket-shaped recess (39c, 39d) in the contacting region (35c, 35d); and/or (m) in the edge regions adjacent to the recess (39c, 39d), the cover element (34) may rest on support elements (38a, 38b).
By applying the measures of the present invention, it is easily possible to prevent mechanical damage to the contacting regions of the detector elements or to the corresponding contacting leads. Thus, this area of the scanning unit can be reliably protected, even when working with a small scanning distance, a small distance between the scanning unit and a scale graduation scanned by it.
In one possible specific embodiment of the scanning unit according to the present invention, it is also possible to realize a very small distance between a radiation-sensitive surface region of a detector element and the required scanning graduations, so that a total system results having an altogether very compact type of construction.
Since the graduation provided in front of the particular intended component is arranged in each case on a separate covering element, this component can be manufactured independently of the carrier element or of the optoelectronic components, ie generally known precision graduation methods can be used for this purpose. On the other hand, it is not possible to pattern encapsulant with this kind of precision.
Furthermore, in another specific embodiment of the scanning unit according to the present invention, besides a graduation on the covering element, an-additional graduation of the component in question can also be provided on its radiation-sensitive or radiation-emitting surface region. It is also possible in such a variant for the components to be additionally designed as an integral component of the carrier element.
Another variant provides for configuring recesses or pockets in the vicinity of the contacting leads on the covering element side. The recesses, i.e., the remaining thickness of the covering element, in these regions are dimensionally sized to protect the contacting leads. This specific embodiment proves to be favorable for miniaturized scanning units, in particular, since an adequate bearing surface is then available for the covering element.
Of course, scanning units designed in accordance with the present invention are able to be used both in conjunction with linear measuring systems, as well as in conjunction with rotary measuring systems.